Heat transfer finned tubing



P 3, 1969 A. c. K. NIHLEN 3,468,372

HEAT TRANSFER FINNED TUBING 3 Sheets-Sheet 1 Filed May 22, 1967 1" .1. 1m. 2- F i/g.fia 15m. 4.

INVENTORS. ARV/D C. K. NIHLEN BY WALTER DORSEY ATTORNE Y5 p 3, 1969 A. c. K. NIHLEN ET AL 3,468,372

HEAT TRANSFER FINNED TUBING Filed May 22, 1967 3 sheets-sheet 2 mygNTORS. ARV/D N/HLEN WALTER ORSEY UM/M ATTORNEYS Sept. 23, 1969 A. c. K. NIHLEN ETAL 3,458,372

HEAT TRANSFER FINNED TUBING Filed May 22. 196 5 Sheets-Sheet 5 38 I I 5114 M A v INVENTORS.

ARV/D c. K. NIHLEN WALTER DORSEY ATTORNEYS United States Patent 3,468,372 HEAT TRANSFER FINNED TUBING Arvid C. K. Nihlen, Wooster, Ohio, and Walter Dorsey, Tulsa, Okla., assignors to The Happy Company, Tulsa, Okla, a corporation of Oklahoma Filed May 22, 1967, Ser. No. 640,114 Int. Cl. F28b 1/36; B21d 53/02 U.S. Cl. 165184 4 Claims ABSTRACT OF THE DISCLOSURE Cross-reference This invention is not related to any pending application.

Summary Finned tubes are used extensively in industry in heat exchanger applications. A finned tube consists basically of a tube through which fluid flows, the tube bearing radial fins upon the exterior surface thereof to increase the heat transfer from the fluid flowing interior of the tubing to liquid or gases exterior of the tube. The manufacture of such fin tubing is also well known. In many applications wherein improved efiiciency of heat transfer is required it is desirable to have a metal to metal heat transfer bond between the tubing and the fin. This is especially true when fluid temperatures exceed 300 F. It has been shown that high cyclic temperatures of a tube have a tendency to expand the fins coiled about it so that the contact pressure between the fin and the tube is greatly reduced. A method commonly used of improving contact between the fin and the tube is to embed and lock the fin into the tubing. Means of accomplishing metal-to-metal bonding of fins to tubing is shown in United States Patent Nos. 2,025,036; 1,914,477; 1,928,639; and others.

In some applications it is desirable for the fin material to function not only as a heat exchange means but, in addition, to provide an armor or covering for the tube to inhibit corrosion. To achieve this benefit a known means includes forming the fin stock during application into an L-shaped configuration having a radial portion and a perpendicular foot portion extending integrally therefrom. The fin material is wound on the tubing such that a foot portion is formed to cover all or at least substantially all of (the exterior of the tube. This has the advantage of providing a sheath or armor for the tube and at the same time increases heat transfer from the tube to the fin material. Such arrangement is shown in United States Patent Nos. 1,829,979; 2,201,024; and others. Obviously the arrangements which provide the best possible heat transfer includes that in which the finned tube not only is of the L- shaped configuration as illustrated in the last mentioned United States patents, but in addition is one in which the fin is locked into engagement with the tube itself. An arrangement wherein the fin stock is formed into L-shaped material and locked at a point intermediate the length of the foot portion is shown in Patent Nos. 3,077,928 and 3,112,558. In the method of the last two mentioned patcuts a spiral groove is formed in the exterior of the tube. Next, one or more pressure rollers are applied to force a portion of the fin stock to cold flow into the groove formed in the tube.

The method of making the fin stock is accomplished by preforming the fin stock into a shape the cross section of which defines a radial fin portion, a foot portion extending perpendicular the radial portion at the lower edge thereof, and an integral boss portion extending from the lower edge of the foot portion in the plane of the radial fin portion, the boss portion being positioned in a spiral groove formed on the surface of a tube. After the boss portion is positioned in the groove on a tube, the tube is contacted by pressure rollers to cold flowing the metal of the tube to engage and lock the fin boss portion. Additionally, in the preferred embodiment, the full length of the foot portion is contacted by a pressure roller to form the foot portion firmly against the exterior of the tubing and in sealing metal-to-rnetal contact abutment with adjacent formed fin strips to provide a sealed armor for the tube.

Description of the views FIGURES 1-4 show the sequential steps of forming an elongated fin stock into a formed fin strip as a portion of the steps in providing a finned tube according to this invention.

FIGURES 5, 6 and 7 are enlarged views of the sequence of steps whereby a straight fin stock is formed into a formed fin strip having a cross-sectional configuration desired for the method of this invention.

FIGURE 8 is a partial cross-sectional view of a length of tubing having a groove formed therein to receive the formed fin stock.

FIGURE 9 is a view showing a tube in cross-section as it is rotated in engagement with rollers to form a spiral groove therein having a configuration as shown in the enlarged cross-sectional view of FIGURE 8.

FIGURE 10 is an enlarged cross-sectional view of a portion of a length of tube having the pre-formed fins of this invention aflixed and bonded to it.

FIGURE 11 is a view showing the means of winding the formed fin strip onto a spiral grooved rotating tube according to this invention.

FIGURE 12 is a cross-sectional view of a tube having engagement with a pressure roller to lockably bond the fin strip to the tube according to the method of this invention.

FIGURE 13 is an enlarged cross-sectional view of a portion of a length of tube as shown in FIGURE 10, but showing an alternate embodiment wherein the integral boss portion of the fin is of a width greater than the width of the fin material.

Detailed description The prior issued patents heretofore referred to in the summary of this invention disclose basically the function and use of fin tubing in heat exchanger applications. This invention provides a method of constructing improved flnned tubing. The method consists basically of four steps, that is: (1) forming a spiral groove on the exterior of a tube to which a fin is to be applied; (2) forming a fin stock into a formed fin strip having, in cross-section, a boss portion; (3) winding the formed fin strip so that the fin strip boss portion extends within the tube spiral groove; and (4) contacting the exterior of the tube and the formed fin strip to lockably bond the fin strip to the tubing. Steps 1 and 2, in the preferred sequence, are per-formed simultaneously by separate mechamsms.

FIGURES 14 show the steps of forming a fin strip stock preparatory to winding upon a tube according to this invention. In FIGURE 1, a metal fin strip stock 10 is fed between two adjacent rollers 12 affixed to a shaft 14. The rollers 12 have a solid center portion 16 therebetween which serves to properly space the fin strip stock. A portion of the fin strip stock extending exterior the circumference of rollers 12 is contacted by a forming roller 18 to initiate bending. A portion of the fin stock is bent to extent perpendicular to the main portion, the perpendicular portion being referred to a the foot portion 20. The formed fin strip stock thus includes a main portion which, when wound upon a tube, extends radially thereto, and will be termed a radial portion 22. A second portion, that is, foot portion 20, is engaged by a second roller 24 as'shown in FIGURE 3. In the step of FIGURE 3, the foot portion is caused to cold flow so that additional metal is concentrated at the intersection of the radial portion 22 and the foot portion 20. In the last step as shown in FIGURE 4, the fin strip stock is subjected to a final forming roller 26 which is essentially of a cylindrical exterior configuration having a reduced diameter groove 28 therein in alignment with the fin radial portion 22. In the step of FIGURE 4 in the final forming roller causes a cold flow at the fin strip stock to produce a boss portion 28 extending in the plane of the radial portion 22 and perpendicularly of the foot portion 20.

Referring to FIGURES 5, 6, and 7, enlarged cross-sections are shown of the fin stock as it travels through the various steps shown in FIGURES 2, 3 and 4, to provide the final formed configuration of FIGURE 7. lengths of the foot portion 20 and radial portion 22 depend upon design and are not limited in any way by the invention. The foot portion may be said to include the full length A as indicated in FIGURE 7 with the radial portion 22 extending upwardly from the foot portion and the boss portion 28 extending downwardly from the foot portion, both in the same planes and perpendicular to the foot portion.

The steps shown in FIGURES 1 through 4 are illustrative of the method of forming the formed fin strip and the same may be accomplished by the use of fewer or a greater number of tools and steps in the actual carrying out of the method. The method relates, in part, to the forming of the fin strip for immediately winding upon a tube and not in the specific tools by which the forming is accomplished since such tools are well within the skill of the art.

A further basic step in the method of this invention includes the provision of a spiral furrow or groove in the exterior surface of the tube to be fitted with fins. The preferred configuration of the groove 34 is shown in the cross-sectional view of FIGURE 8. FIGURE 9 illustrates means whereby the groove 34 may be formed in the tubing. The tubing is rotated relative to spaced forming rollers 36A, 36B and 36C, each of which have a circumferential configuration progressively displacing metal in the exterior surface of tubing 30. As shown in FIGURES 8 and 9, the preferred configuration of groove 34 is formed in such a way that a substantial portion of the displaced metal is cold flowed to one side of the groove 34 forming, in the tube cross-section, a peak 38. The method of forming groove 34 is illustrated in FIG- URE 9 for purposes of exemplification only and the invention is not limited to such a means of forming the groove 34 as such may be formed in a variety of ways well within the skill of the art.

- As has been previously indicated, the forming of the fin strip stock 10 into the desired form as described with reference to FIGURES 1 through 7 is preferably carried out simultaneously with the formation of the spiral groove 34 in the tube 30 as shown in FIGURES 8 and 9. The next basic step in the method of this invention is the winding of the formed fin strip onto the exterior of the tubing 30, which is accomplished by simultaneously rotating and axially advancing the tube 30 relative to the formed finned strip causing the fin strip to wind spirally thereon. Means whereby this is accomplished is illustrated in FIGURE 11 which shows the formed fin strip, indicated generally by the numeral 49, being wound on rotating tube 30. Guide rollers 42 and 44 have a slot The 46 therebetween which receives the radial portion 22 of the formed fin strip to guide it properly upon the tube The formed fin strip 40 is wound upon tubing 30 so that the fin strip boss portion 28 is received within the groove 34. The foot portion 20 of the fin strip lies parallel to and contiguous to the exterior surface of the tubing 30 and in the preferred arrangement the foot portion 20 is of a total length equal the lead of the spiral groove 30 so that the foot portion 20 lies mutually contiguous at each end.

After the strip is wound in proper position on the exterior of tubing 30, the next step of the method'ineludes contacting the formed fin strip by pressure rollers as the tube is rotated to cold flow and level the metal of the exterior surface of the tube to lockably bond the fin strip to the tube. This is illustrated in FIGURE 12 wherein rollers 42 and 44 are pressed against the wound fin strip 40. Roller 42 engages the upper surface 48 of foot portion 20 along its full length between adjacent fin radial portions 22. The slot 46 between rollers 42 and 44 maintain the radial portion 22 of the fin perpendicular the longitudinal axis of tube 30. Forming roller 44 is of slightly larger diameter than roller 42 and engages the exterior surface of tubing 30 adjacent the radial portion 22 of the formed fin strip immediately after it is wound onto the tube 30. The roller 44 cold flows and flattens the peak 38 to lock the formed fin strip boss portion 28 into groove 34. At the same time forming roller 42 cold flows the foot portion 20 of the formed fin strip to sealably engage the adjacent spiral fin strip portions to provide a sealed metal to metal engagement at points A of FIGURE 12. In this way the foot portion 20' of the fin strip completely sealably covers the total exterior surface of tube 30.

An enlarged cross-sectional view of the finned material 40 having been wound upon a tubing 30 and contacted by pressure roller to achieve the desired cold flow of metal shown in FIGURE 10. The formed fin strip 40 is embedded in the exterior surface of tube 30 and locked to the tube by the cold flow of metal of the tube against the fin strip boss portion 28. The foot portion 20 of the fin strip is in metal-to-metal contact with the adjacent foot portion at points A so that the foot portion 20 of the wound fin material completely covers the exterior of the tubing 30 providing a sealed armored cover. Radial portion 22 of the spiral wound fin strip extends perpendicular the longitudinal axis of tube 30.

The method and the product accomplished thereby provides a finned tube having superior characteristics especially when used in high temperature applications. First, the fin strip is securely bound to the tube to a degree not achievable with the heretofore used methods. The possibility of the fin strip becoming dislodged from the tubing is, for all practical purposes, eliminated. Second, because of the superior mechanical bonding of the fin strip with the tubing greater heat transfer characteristics are obtained. Third, the fin strip material completely covers the tube in a metal-to-metal seal arrangement. Thus a relatively inexpensive tube of material such as steel can be covered with fin strip material having noncorrosive characteristics, such as aluminum, to permit the usage of steel tubing in corrosive environments. Four, the provision of means wherein the fin strip is mechanically bonded to the tubing in the plane of the radial portion of the fin strip means that the shortest possible length of heat flow gradient is obtained from the tube to the radial fin portion 22. These combinations of advantages are not obtainable in any other method of manufacturing finned tubing presently known.

FIGURE 13 shows an alternate embodiment of the invention. In the illustrated embodiment of the invention as shown in FIGURES 1 through 12 the integral boss portion 28 is shown as being formed as having a width the same as the thickness of the fin material. This is optional as the boss portion 28 may be of a greater width (as measured by the distance B in FIGURE 13) than the fin material or radial fin portion 22 (as measured by the distance C in FIGURE 13). The configuration of FIGURE 13 requires the groove 34 formed in the tube 30 to be of corresponding increased width. The wider boss portion is formed in the same way as shown generally in FIGURES 1 through 4 except that in FIGURE 4 the groove 28 in final forming roller 26 is correspondingly wider.

It is well known that the thermal conductivity of steel of which tubes 30 are generally formed, is less than that of aluminum, of which fins 40 are generally formed.

The embodiment of FIGURE 13 permits the size of the boss portion 28 to be proportioned so that the thermal conductivity of the contact area of the steel tube 30 matches the thermal conductivity of an aluminum fin radial portion 22 to achieve maximum heat transfer efficiency.

The invention has been described with reference to exemplified embodiments, it being understood that the invention is not limited to such illustrated and exemplified embodiments which are use to assist in the explanation of the invention, nor is the invention limited to the abstract nor the summary included herein, but the invention is that encompassed in the attached claim or claims, including all of the equivalents to which each element or step of the attached claim or claims is entitled.

What is claimed:

1. A heat transfer tube comprising:

a metal tube having a constant lead spiral groove scored in the exterior surface;

a fin strip defined in the cross-section thereof perpendicular the length thereby by an upstanding radial portion,

an integral foot portion extending perpendicular the radial portion at the lower edge thereof,

said foot portion being equal to the lead of said spiral groove with the end thereof being in metal to metal contact with the back of said radial portion,

a boss portion extending integrally downwardly from the lower edge of said foot portion and in the plane of said radial portion,

said fin strip spirally aflixed to the exterior of said tube, the boss portion thereof embedded within said spiral groove in said tube in metal to metal interlocking relationship, the full length of said foot portion of said fin strip contacting the exterior surface of said tube.

2. A heat transfer tube according to claim 1 wherein the length of said foot portion which is equal to the lead of said spiral groove is an exterior surface of said tube and wherein the outer ends of said fin strip foot portions sealably abuts one another providing a sealed metal to metal armor of the exterior of said tube.

3. A heat transfer tube according to claim 1 wherein said spiral groove includes opposed side walls and wherein a portion of said tube along one wall of said spiral groove protrudes into said fin strip integral boss portion locking said boss portion to said tube.

4. A heat transfer tube according to claim 1 wherein the width of said integral boss portion of said fin strip measured in a plane of the tube axis is greater than the width of said fin upstanding radial portion measured in the same plane.

References Cited UNITED STATES PATENTS 1,928,639 10/1933 Berg 29-1573 2,525,092 10/1950 Bruegger 165-184 X 3,077,928 2/ 1963 Nihlen et al. l184 FOREIGN PATENTS 415,609 8/1934 Great Britain.

ROBERT A. OLEARY, Primary Examiner T. W. STREULE, Assistant Examiner US. Cl. X.R. 29-4573 

